One method of joining two structural members together is by the use of an adhesive at the interface between the two members. The adhesive typically transfers shear load between the members via an adhesive bond. This bond is critical, and requires considerable effort in both manufacturing and inspection. Despite the best efforts, use of adhesive bonds in aircraft and other primary structures is very difficult to certify, due to the catastrophic failure mode of a debonded joint. The only proven way around this pervasive problem is to bolt the bonded joint together with mechanical fasteners, which removes many advantages of the bonded joint, particularly when the joined members are composite.
It is important during the bond assembly process that the adhesive extend throughout the bonding surface, preferably at a uniform thickness. This is difficult to accomplish at times, leaving spaces or areas that do not have adhesive. Speeding the process up would be desirable to reduce costs.